Aftertreatment of wet spun acrylonitrile polymer filaments with aqueous zinc oxide solution



Oct. 30, 1962 J. D. VEITCH 3,061,398

AFTERTREATMENT 0F WET SPUN ACRYLONITRILE POLYMER FILAMENTS WITH AQUEOUS ZINC OXIDE SOLUTION 2 Sheets-Sheet 1 Filed April 22, 1960 whmoow m JOK mu mo INVENTOR. JOHN D. VEITCH A T TOR/VE'Y DYE ABSORBED ON FIBER Oct. 30, 1962 J. D. VEITCH 3,061,398

AFTERTREATMENT OF WET SPUN ACRYLONI'IRILE POLYMER FILAMENTS WITH AQUEOUS zmc OXIDE SOLUTION Filed April 22. 1960 2 Sheets-Sheet 2 SPIN AND COAGULATE WASH STRETCH IMPREGNATE WITH ZnO DRY zmc OXIDE IMPREGNATED FILAMENT CONTROL l I l l I l l I IO 3O 4O 6O 8O I00 T|ME(M|NUTES) AT BOIL 91 4- EVE-72% A T TOR/V5 Y United States Patent Ofifice 3,061,398 Patented Oct. 30, 1962 of Delaware Filed Apr. 22, 1960, Ser. No. 24,086 3 Claims. (Cl. 8-97) This invention relates to the treatment of acrylonitrile polymer filamentary material, e.g. strands, yarns, tows, and like funicular structures. More particularly, this invention relates to the treatment of wet-spun acrylonitrile polymer filaments after the manufacture thereof to impart improved dyeability and anticorrosive properties thereto and to the product resulting therefrom.

In view of the high-melt viscosity and the thermal sensitivity of acrylonitrile polymers, acrylic filaments are prepared commercially either by the dry-spinning process or by the wet-spinning process rather than by the melt spinning technique, as is well known. In thewet-spinning process of producing acrylonitrile filamentary material, a polymer solution is extruded through a spinneret or equivalent extrusion devices into a suitable coagulating liquid that will extract the solvent from the solution and precipitate the polymer in the form of filaments. The coagulating liquid which may be aqueous or polymeric glycol baths and the likemay be maintained so as to have 'a predetermined and desired content of the solvent in its composition. The coagulated filaments are withdrawn from the coagulating liquid and are'stretched to obtain a desired orientation according to various techniques. The filaments are generally subjected to a washing operation which may be carried out by passing the filaments through a water bath, by spraying the material with water, or by other various techniques. The purpose of the washing is to rid the coagulated filaments of residual solvent as much as practicable. In addition to the washing and stretching operation, the filaments are impregnated with a textile finishing composition for imparting antistatic, lubricity, softness and like properties to the filaments to facilitate processing of the same in such subsequent operations as spinning, twisting, winding, reeling, Warping, carding, drafting, weaving and others.

it is known that textile materials comprising filaments or fibers of acrylonitrile polymers suffer a drawback as compared to some other filaments or fibers in that they cannot be dyed satisfactorily by conventional dyeing processes as would be desired by the trade. Many expedients have been suggested to encourage dye penetration and retention in such materials.

A disadvantage of the use of filaments or fibers wet spun from acrylonitrile polymers dissolved in N,N-dimethylacetamide or the like is that they tend to be corrosive to metal upon contact therewith. Hence, they cause considerable difi'iculty and give rise to added expense during the handling of the same during spinning, twisting, carding, etc.

The corrosive characteristic and the unsatisfactory dyeability of acrylonitrile polymer filaments have led to a great deal of study and research to correct these properties. As a result various remedies have been proposed to impart non-corrosive properties thereto, but they have not been very efiicient because these procedures suffer -.and being non-corrosive to the metal used in textile processing apparatus.

It is another object of the present invention to provide a process for treating acrylonitrile filamentary materials so as to render same more dyeable and less corrosive to metal used in textile processing apparatus.

It is a further object of the present invention to provide an inexpensive treatment of wet-spun filaments of acrylonitrile polymer during the manufacture thereof, whereby the filaments are rendered more dyeable and less corrosive to metals used in textile processing apparatus.

Other objects will be apparent from the following description and claims.

The objects of this invention may be accomplished by mixing zinc oxide with a volatile carrier such as water to form a suspension or solution thereof and immersing the filaments of acrylonitrile polymer in, or passing same through, the resulting mixture for a length of time sufficient to enable the filaments to become impregnated with the mixture. Thereafter, the filaments are removed; and the volatile carrier is evaporated so as to leave the filaments dry and impregnated with zinc oxide. It has been discovered that the filaments so treated have a higher rate of dyeing with basic dyes and that comparative dying indicates that the zinc oxide-containing filaments also have a higher rate of dyeing with dispersed dyes. Another aspect of the discovery is that the treatment leads to the production of filaments that have no corrosive action on metal and metal alloys upon which they may come into contact during the handling of same into fabric and the like.

By acrylonitrile polymer is meant polyacrylonitrile,

copolymers, and terpolymers of acrylonitrile, and blends of polyacrylonitrile and copolymers of acrylonitrile with other polymerized mono-olefinic materials, as well as blends of polyacrylonitrile and such copolymers with small amounts of other polymeric materials, such as polystyrene. In general, a polymer made from a monomeric mixture of which acrylonitrile is at least percent by weight of the polymerizable content is useful for preparing filaments and fibers. Besides polyacrylonitrile, useful copolymers are those of or more percent of acrylonitrile and one or more percent of other mono-olefinic monomers. Block and graft copolymers of the same general type are also useful. Suitable other monomers include vinyl acetate, and other vinyl esters of monocarboxylic acids, vinylidene chloride, vinyl chloride and other vinyl halides, dimethyl fumarate and other dialkyl esters of fumaric acid, dimethyl maleate and other dialkyl esters of maleic acid, methyl acrylate and other alkyl esters of acrylic acid, styrene and other vinyl-substituted aromatic hydrocarbons, methyl methacrylate and other alkyl esters of methacrylic acid, vinyl-substituted heterocyclic nitrogen ring compounds, such as the vinyl imidazoles, etc., the alkyl-substituted vinylpyridines, vinyl chloroacetate, allyl chloroacetate, methallyl chloroacetate, allyl glycidyl ether, methallyl glycidyl ether, allyl glycidyl phthalate, and the corresponding esters of other aliphatic and aromatic dicarboxylic acids, glycidyl acrylate, glycidyl methacrylate, and other mono-olefinic monomers copolymerizable with acrylonitrile.

Many of the more readily available monomers for polymerization with acrylonitrile form copolymers which are not reactive with some dyestuffs and may therefore be impossible or diificult to dye by conventional techniques. Accordingly, these non-dyeable fiber-forming copolymers may be blended with polymers or copolymers which are in themselves more dye-receptiverby reason of their physical structure or by reason of the presence of functional groups chemically reactive with the dyestuif, whereby the dyestuff is more permanently bonded to the polymer in a manner which lends resistance to removal thereof by the usual laundering and dry cleaning pro- 3 cedures. Suitable blending polymers may be polyvinylpyridine, polymers of alkyl-substituted vinylpyridine, polymers of other vinyl-substituted N-heterocyclic compounds, the copolymers of the various vinyl-substituted N-heterocyclic compounds and other copolymerizable monomers, particularly acrylonitrile.

Of particular utility are the blends formed of polyacrylonitrile or a copolymer of more 90 percent acrylonitrile and up to 10 percent vinyl acetate, and a copolymer of vinylpyridine or an alkyl-substituted vinylpyridine and acrylonitrile, the said acrylonitrile being present in substantial proportions to provide heat and solvent resistance, and a substantial proportion of the vinylpyridine or derivatives thereof to render the blend receptive to dyestuffs. Of particular utility are the blends of copolymers of 90 to 98 percent acrylonitrile and 10 to 3 percent vinyl acetate and sufiicient copolymer of 10 to 70 percent acrylonitrile and 90 to 30 percent vinylpyridine to produce a blended composition with a total of 3 to 10 weight percent vinylpyridine.

The polymers just described may be prepared by any conventional polymerization procedure, such as mass polymerization methods, solution polymerization methods, or aqueous emulsion methods. The polymerization is normally catalyzed by known catalysts and is carried out in equipment generally used in the art. However, the preferred practice utilizes suspension polymerization wherein the polymer is prepared in finely dividcd form for immediate use in the filament-forming operations. A preferred suspension polymerization involves batch procedures, wherein monomers are charged with an aqueou medium containing the necessary catalyst and dispersing agents. A more desirable method involves the semi-continuous procedure in which the polymerization reactor containing the aqueous medium is charged with the desired monomers gradually throughout the course of the reaction. Entirely continuous methods involving the gradual addition of monomers and the continuous withdrawal of polymer can also be employed.

The polymerization is catalyzed by means of watersoluble salts of peroxy acids, sodium peroxide, hydrogen peroxide, sodium perborate, sodium salts of other peroxy acids, and other water-soluble compounds containing the peroxy group:

A wide variation in the quantity of peroxy compound is possible. For example, from 0.1 to 3.0 percent by weight of the polymerizable monomers may be used.

The so-called redox catalyst system also may be used.

Redox agents are generally compounds in a lower valent state which are readily oxidized to the higher valent state under the conditions of reaction. Through the use of this reduction-oxidation system, it is possible to obtain polymerization to a substantial extent at lower temperatures than otherwise would be required. Suitable redox agents are sulfur dioxide, alkali metal and ammonium bisulfites, and sodium formaldehyde sulfoxylate. The catalyst may be charged at the outset of the reaction, or it may be added continuously or in increments throughout the reaction for the purpose of maintaining a more uniform concentration of catalyst in the reaction mass. The latter method is preferred because it tends to make the resultant polymer more uniform in its chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable to promote the uniform distribution of reagents by using inert wetting agents, or emulsion stabilizers. Suitable reagents for this purpose are the water-soluble salts of fatty acids, such as sodium oleate and potassium stearate, mixtures of water-soluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of triethanolamine and dodecylmethylamine, salts of rosin acids and mixtures thereof, the water-soluble salts of half esters of sulfonic acids and long chain aliphatic alcohols, sulfonated hydrocarbons, such as alkyl 'aryl sulfonates, and any other of a wide varieyt of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agent will depend upon the particular agent selected, the ratio of monomer to be used and the conditions of polymerization. In general, however, from 0.1 to 1.0 weight percent based on the weight of the monomers can be employed.

The emulsion polymerizations are preferably conducted in glass or glass-lined vessels provided with means for agitating the contents therein. Generally, rotary stirring devices are the most effective means of insuring the intimate contact of the reagents, but other methods may be successfully employed, for example, by rocking or rotating the reactors. The polymerization equipment generally used is conventional in the art.

The optimum methods of polymerization for preparing fiber-forming acrylonitrile polymers involve the use of polymerization regulators to prevent the formation of polymer units of excessive molecular weight. Suitable regulators are the alkyl and aryl mercaptans, carbon tetrachloride, chloroform, dithioglycidol and alcohols. The regulators may be used in amounts from 0.001 to 2.0 percent, based on the weight of the monomer to be polymerized.

The polymers from which the filaments are produced in accordance with the present invention have specific viscosities within the range of 0.01 to 0.40. The specific viscosity value, as employed herein, is represented by the formula:

Viscosity determinations of the polymer solutions and solvent are made by allowing said solutions to fiow by gravity at 25 C. through a capillary viscosity tube. In the determinations herein, a polymer solution containing 0.1 gram of the polymer dissolved in 100 ml. of N,N-dimethylformamide was employed. The most effective polymers for the preparation of filaments are those of uniform physical and chemical properties and those of relatively high molecular weight.

In a preferred embodiment of the present invention the treatment of the acrylonitrile polymer filaments with zinc oxide is carried out after wet spinning of the filaments and during the aftertreatment of the freshly-spun filaments but before the initial drying of the filaments. Care is taken that the drying of the filaments is accomplished in the presence of the zinc oxide. Hence, according to one aspect of the invention the acrylonitrile polymer as above defined is dissolved in a suitable solvent to form a spinning solution. Suitable solvents include N,N-dimethylformamide, N,N-dimethylacetamide, gamma-butyrolactone, ethylene carbonate, certain watersoluble inorganic salts, and others known in the art, the first two mentioned solvents being preferred. The spinning solution can be prepared by heating and stirring a mixture of a finely divided acrylonitrile polymer of the type described above. The solution of acrylonitrile polymer is extruded through a desired number of orifices in a spinneret disposed just above or in a liquid coagulating medium which is a solvent for the solvent used to dissolve the polymer and a precipitant for the polymer in the spinning solution. The filaments produced may be stretched in the coagulating bath before being removed therefrom. After removal thereof from the coagulating bath, the filaments are stretched to obtain a desired orientation according to various ways. The filaments are washed to rid same of residual solvent, the washing may be accomplished in various ways as indicated above. Before being dried the filaments are directed through a liquid bath containing a finishing composition. Since it is generally necessary to apply a finish to wet-spun acrylonitrile polymer filamerts during the aftertreatment thereof for one or more purposes, such as lubricating the filaments, reducing the development of static electricity thereon, etc., the zinc oxide is preferably added to the finishing composition. Any conventional filament finishing composition is satisfactory and the selection of a particular finishing composition is not necessary to the proper practice of the present invention.

When Zinc oxide is incorporated in a finishing composition, it is preferred that the finish be an aqueous emulsion. The solids content of the finishing compositions other than zinc oxide is preferred to be composed of about 20 to 50 percent by weight of a non-ionic surface active ester, from 15 to 35 percent of a non-ionic surface active polyether, from to 40 percent of a cationic surface active quaternary ammonium compound, and from 5 to 25 percent of a substituted carbamyl derivative. This preferred finishing composition is described in US. Patent No. 2,735,790.

It is not necessary to the invention that the Zinc oxide be incorporated in a finishing composition. The same enhanced dyeability and non-corrosive property can be attained by passing the filaments through an aftertreating bath containing only the zinc oxide in solution or suspension, as long as the filaments are impregnated with zinc oxide. For convenience, the zinc oxide may be incorporated into the usual finishing bath, thereby accomplishing the same effect without subjecting the filaments to an additional aftertreating step. However, it is possible and sometimes desirable to pass the filaments first through a bath containing zinc oxide in solution and immediately through a finish bath containing a small amount of zinc oxide. The filaments are passed through the finish bath in such a manner that the Zinc oxide ingredient deposited on the filaments by the first applied liquid is not entirely washed out.

The filaments containing the Zinc oxide are dried, preferably by application of heat. For example, the filaments may be dried by passing the same around a battery of dry rolls or cans.

The impregnating of the filaments is preferred to be carried out during the aftertreatment while the filaments are in continuous form; but, of course, this is not essential to the invention. For example, the filaments after being stretched may be cut into staple fibers. A blanket of fibers is carried progressively on a flat conveyor whereon the fibers may be spray washed. Thereafter the blanket of fibers is passed under a shower of liquid finishing composition containing zinc oxide. Then, the fibers are dried as, for example, in a conventional convection dryer or the like. The fibers are thus dried while they have a small amount of zinc oxide incorporated therein, Whereby the fibers have enhanced dyeability and are inert to metals of the type used in textile processing apparatus.

While the best method of carrying out the invention has been described, the impregnation can be carried out in conventional fabric treating equipment as well.

Generally, the application of zinc oxide may be conducted conveniently by passing the filaments through a liquid bath at atmospheric pressure, though other pressures may be employed. Room temperature is satisfactory but elevated or lower temperatures may be employed.

Zinc oxide is incorporated into the acrylonitrile polymer filaments in the amount of at least 0.01 percent of the latter and up to 0.40 percent and higher as zinc oxide or other zinc compounds. The preferred amounts of zinc compound addition are within the range of 0.025 to 0.20 percent based on the weight of the polymer, it being desirable to use only the minimum amount of zinc oxide necessary to obtain the desired efiect since excess addition of zinc oxide is an added expense.

and 0.5% Igepal CO-710.

The concentration of zinc oxide inthe liquid impregnating bath can be varied considerably, as can be perceived. The concentration will depend upon the particular method of application, the proportion of the liquid picked up by the filaments, the composition of the finish, etc. Baths containing 0.02 percent to 0.8 percent zinc oxide give incorporation of 0.01 to 0.40 percent of zinc oxide based on the dry filaments.

While it is preferred that the volatile carrier for the zinc oxide be water, it is apparent that other volatile materials inert to the filaments can be used to dissolve or suspend the zinc oxide so that same may be advantageously incorporated in the filaments.

After impregnation is accomplished, the excess liquid can be removed by squeezing or the like and then the filamentary material is dried. Drying may be accomplished by heating the zinc oxide-containing material, for example, at a temperature of C. to 245 C., for a time suificient to dry the filaments.

In the attached drawing, FIGURE 1 is a perspective view of a section of an acrylonitrile polymer filament having a small amount of zinc oxide incorporated there- FIGURE 2 is a side elevational view partly in section showing schematically an apparatus arrangement of a type which can be used in carrying out one aspect of the process of the present invention. Reference numeral 10 designates a tow of acrylic filaments which have been molecularly oriented. This tow of filaments is forwarded by means of godets 11 through a suitable tank 12 for containing a bath 13 of zinc oxide suspension. After being passed through the zinc oxide-containing bath for a sufficient distance, the tow is removed therefrom and passed over a plurality of heated dryer rolls 14. After being dried, the tow 10 may then be subjected to further operations such as crimping, cutting and baling, or the tow may be collected in continuous form. Additional bath is supplied to tank 12 by means of conduit 15,as needed.

FIGURE 3 is a flow sheet diagram illustrating one practice of this invention from a manipulative step viewpoint. The acrylonitrile polymer solution is spun and coagulated. The filaments so produced are washed and stretched. After these steps, the filaments are then treated by impregnating same with the liquid bath containing Zinc oxide. Thereafter, the filamentary material is dried at an elevated temperature.

FIGURE 4 is a diagram which shows the comparison between the dye absorbed by the fibers impregnated with zinc oxide as compared with like fibers which have not been impregnated with zinc oxide. The axis of ordinates is the dyeing time at boil in minutes and the axis of abscissas is the percent of dye absorbed in the fibers. The dye employed in this comparison is 8% Sevron Blue 2G It is indicated from the diagram that the fibers containing zinc oxide display a higher tendency to absorb dyes.

The following examples, in which parts and percentages are given by weight unless otherwise indicated, illustrate preferred methods of carrying out the treatment in accordance with this invention. The invention is not to be limited by details set forth in the following examples.

EXAMPLE I A copolymer composed of 94 percent acrylonitrile and 6 percent vinyl acetate was dissolved in the solvent composed of 98% N,N-dimethylacetamide and 2% acetic acid. The resulting polymer was extruded through a spinneret immersed in an aqueous coagulating bath containing about 55 percent of the solvent and 45 percent water. The filaments so produced had total denier of about 360,000. This tow of filaments was passed through a hot water bath moving counter-currently with respect to the directional movement of the tow and was given an orientation stretch at the same time of about 525 percent. Next the tow was passed continuously through a bath containing a finishing composition in which zinc oxide was incorporated. The bath was an aqueous emulsion containing a 2.2 percent non-aqueous finishing composition and 0.25 percent of zinc oxide as zinc. The finish composition comprised sorbitan monopalmitate, castor oil condensed with about 200 moles of ethylene oxide and a quaternary anti-static agent. Thereafter, the tow was passed around a battery of dryer rolls internally heated with steam at 4-0 p.s.i.g. It was found that the dried filaments contained 0.27 percent zinc compounds as zinc by weight. The tow was crimped and cut into staple fibers. The fibers were carded on a conventional carding machine. The fibers displayed no corrosive action on the metal of such machine even after extended contact therewith.

EXAMPLE II Filaments were produced in the manner described in Example I. However, in this instance the emulsion finishing bath did not contain any zinc oxide. During carding of the fibers corrosion due to the contact of the fibers with the carding machine was observed.

EXAMPLE III A 480,000 denier tow of wet-spun filaments of the type described in Example I and which had been stretched was passed through a bath composed of water and 0.13 percent zinc oxide as zinc. Thereafter, the filaments were sprayed with water and passed through a finish bath containing 2.2% of the non-aqueous constituents described in Example I and 0.03 percent zinc oxide as zinc. The

tow was dried by passing it around a battery of dryer rolls. It was found that the dried filaments contained 0.15 percent zinc compounds as zinc. The tow was crimped and cut into staple fibers. It was found that the fibers were not corrosive to a conventional carding machine.

EXAMPLE IV dyed. The sample to be dyed was placed in the oath pre- I pared for it and the temperature of the dyebath was slowly raised to boil and held there for the periods of time in minutes indicated in Table 1 below. The first set of data in Table 1 represents the results obtained with the tapes woven from the zinc oxide treated acrylonitrile polymer filaments of Example I; and the second set of data represents the results obtained with the tapes woven from acrylonitrile polymer filaments of Example II which were not treated with zinc oxide. For convenience the heading of the first set of data is presented as ZnO containing Filaments; and the heading of the second set of data is presented as Control Filaments. The percent dye absorbed and the percent exhaust of the bath were determined for each tape dyed. In the column captioned Percent Dye Absorbed the data for the given dyeing times denote that the 8.0% content of Sevron Blue 2G dye of the prepared dyebath has been reduced by the percent indicated. For example, in the first set of data after minutes at boil, the dye bath had a remaining Sevron Blue 26 content equivalent to a dye bath containing 5.9 percent of this dye. In the column captioned Percent Exhaust the data indicate on a weight basis the percentage of the dye in the dye bath which has been removed therefrom by the fabric at a given time in minutes. The following results were obtained,

Table ZuO CONTAINING FILAMENIS Percent Percent Time at Boil (Min) Dye :rlmust Absorbed 2. l 2:). S 3. 2 4 l. 2 4. l 5L0 4. 7 5S. 8 5. 2 05. i 5. 7 Tl. 7 0.1 70. S 0. 5 81. l 6. 8 84. 6 7'. 0 67. 5

CONTROL FILAMENTS Percent Percent Time to Boil (Min) Dye Exhaust Absorbed 1. 5 18. 4 2.2 27.0 2. 6 33. 0 3.0 37. 9 3. 3 41. S 3. 5 43. 7 3. 7 lli. l 15. 9 4S. 8 -l. 0 50. 0 4. 3 53. 3

From the foregoing data it is indicated that acrylonitrile polymer filaments having zinc oxide impregnated therein exhibit a faster dyeing rate with basic dyes, as compared with similar filaments which do not contain zinc oxide. To determine the relationship of the relative dycing rates, the percent dye absorbed was plotted against the square root of time. From the slopes of the lines connecting the plotted points, it was calculated that the zinc oxide-containing filaments had approximately a 60% higher dyeing rate than the filaments having no zinc oxide impregnated therein.

EXAMPLE V A series of competitive dyeings (both sample and control dyed in the same dyebath) was made for minutes at the boil. Again all dyeings were made in a 40:l bath with percentages being based on the weight of fabric. Tapes of standard construction woven from spun yarn of the fibers in Examples I and II were employed. The sample (Example I) and control (Example II) were graded visually for dye level (depth of shade) using the International Gray Scale. The dyeings were made with:

1) Three selected basic dyes at 4.0% depth and the black compound shade (see Table 2 below).

Dyes with:

5% ammonium acetate 0.5% Igepal CO-7l0 (2) Two selected disperse dyes at 4% depth and a navy compound shade (see Table 2 below).

Dyes with: 0.5% Igepal T-Sl The dye level ratings of tapes for these dyes are given in Table 2 below, in which a rating of 5 is given for the filaments dyed the heaviest. The filaments are given a comparative rating of 4-slightly lighter, 3-noticeably lighter, Z-considerably lighter, and l-much lighter. In Table 2 the set of data listed as Sample in the Dye Level column represents the results obtained with the tapes woven from the zinc oxide treated acrylonitrile polymer filaments of Example I. The set of data listed as Control in the Dye Level column represents the results obtained with the tapes woven from acrylonitrile polymer filaments of Example 11 which were not treated with zinc oxide.

9 Table 2 Dye Level Percent Dyestufi Sample Control Basie Dyes:

4.0% Sevron Brilliant Red 4G 4.0% Sevron Blue B 30% Sevron Orange R Navy:

4.0% Celliton Navy Blue BBG 5 4 1.0% Celliton Fast Black BGA 0.6% Latyl Cerise B 0.4% Amacel Yellow CW Thus, it is noted that the zinc oxide impregnated filaments dye considerably heavier with basic dyes and heavier with disperse dyes than filaments that did not contain zinc oxide, indicating a higher rate of dyeing.

Thus, it is seen the use of zinc oxide has several advantages. Acrylonitrile polymer filaments containing zinc oxide are rendered substantially non-corrosive to metal and therefore may be handled by textile processing apparatus without giving rise to injury to such apparatus due to corrosion. Furthermore, the filaments treated with zinc oxide have a higher dyeing rate with basic dyes (60% higher with Sevron Blue 2G for example) than filaments not so treated. Zinc oxide-containing filaments dye slightly heavier with disperse dyes, indicating a higher rate of dyeing. Another advantage is that zinc oxide is a common chemical readily available in commercial quantities at moderate prices. Zinc oxide is readily incorporated into the finish bath employed in the aftertreatment of wetspun acrylic filaments. Furthermore, the amounts of zinc oxide employed do not affect the stability of conventional finishing solutions. In addition the use of zinc oxide presents no operational hazards and requires no major equipment changes. Also, the light stability of the treated material is increased.

Any modification of the procedure described herein which conforms to the principles of the invention is intended to be included within the scope of the appended claims.

What is claimed is:

l. A method of aftertreating filaments wet spun from an acrylonitrile polymer dissolved in a solvent selected from the group consisting of N,Ndimethylformamide and N,N-dimethylacetamide consisting of the steps of continuously stretching said filaments to increase the molecular orientation thereof and washing said filaments to rid same of residual solvent, then continuously passing said stretched filaments through a bath composed of a mixture of water and zinc oxide to impregnate the said stretched filaments with said mixture, the zinc oxide being present in said mixture in an amount of about 0.02 to 0.8 percent based on the weight of the bath, and thereafter drying for the first time the impregnated filaments with application 10 of heat so as to leave the filaments dry and impregnated with about 0.01 to 0.4 percent zinc oxide based on the weight of the filaments, thereby imparting improved dyeability and anti-corrosive properties to the filaments so treated, said acr'ylonitrile polymer being composed of at least percent by weight polymerized acrylonitrile.

2. A method of aftertreating filaments wet spun from an acrylonitrile polymer dissolved in a solvent selected from the group consisting of N,N-dimethylformamide and N ,N -dimethylacetamide consisting of the steps of continuously stretching said filaments to increase the molecular orientation thereof and washing said filaments to rid same of residual solvent, then continuously passing said stretched filaments through a finishing bath composed of a mixture of Zinc oxide and an aqueous emulsion of a textile finish to impregnate said stretched filaments with said mixture, the zinc oxide being present in said mixture in an amount of 0.02 to 0.8 percent based on the weight of the bath, and thereafter continuously drying for the first time the impregnated filaments with application of heat so as to leave the filaments dry and impregnated with about 0.01 to 0.4 percent zinc oxide based on the Weight of the filaments, thereby imparting improved dyeability and anti-corrosive properties to the filaments so treated, said acrylonitrile polymer being composed of at least 70 percent by weight polymerized acrylonitrile.

3. A method of aftertreating filaments wet spun from an acrylonitrile polymer dissolved in a solvent selected from the group consisting of N,N-dimethylforrnamide and N,N-dimethylacetamide consisting of the steps of continuously stretching said filaments to increase the molecular orientation thereof and washing said filaments to rid same of residual solvent, then continuously passing said stretched filaments through an aqueous bath containing 0.02 to 0.8 percent zinc oxide to impregnate said fila ments with zinc oxide, then passing said stretched filaments through a finishing bath composed of a mixture of zinc oxide and an aqueous emulsion of a textile finish to impregnate said filaments with said mixture, the zinc oxide being present in said mixture in an amount of 0.1 to 0.8 percent based on the weight of the finishing bath, and thereafter drying for the first time the impregnated filaments with application of heat so as to leave the filaments dry and impregnated with 0.01 to 0.4 percent zinc oxide based on the weight of the filaments, thereby imparting improved dyeability and anti-corrosive properties to the filaments so treated, said acrylonitrile polymer being composed of at least 70 percent by weight polymerized acrylonitrile.

References Cited in the file of this patent UNITED STATES PATENTS 1,983,349 Dreyfus Dec. 4, 1934 2,438,968 Feild et al Apr. 6, 1948 2,643,986 Ham et al June 30, 1953 2,734,835 Florio et al. Feb. 14, 1956 2,759,851 Fluck et al. Aug. 21, 1956 2,805,959 Ewing Sept. 10, 1957 2,952,651 Armen et a1. Sept. 13, 1960 

1. A METHOD OF AFTERTREATING FILAMENTS WET SPUN FROM AN ACRYLONITRILE POLYMER DISSOLVED IN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF N,N-DIMETHYLFORMAMIDE AND N,N-DIMETHYLACETAMIDE CONSISTING OF THE STEPS OF CONTINUOUSLY STRETCHING SAID FILAMENTS TO INCREASE THE MOLEC- 